Method of forming a weld fitting

ABSTRACT

A coupling for use in forming a welded tube joint is disclosed along with a method for forming such joint. A thin coupling sleeve is tightly swage-fitted onto the end of a tube to form a male or female tube end assembly suitable for engagement with a tubular mating part assembly which may be a fitting or another coupling sleeve and tube assembly. The male-female interlocking arrangement provides radial and axial alignment of the joined assemblies. The structure is arranged to provide a space between the tube end face and the interior end face of the tubular mating part assembly. During the welding operation, external fusion heat is applied to form a single weld bead extending from the interior of the tube to the exterior surfaces of the assemblies. The width of the weld at its inner radial extremities is longer than the axial width of the space between the interior end faces and its width at its outer radial extremities is at least equal to twice the axial length of the male-female telescoped portion so that all the members are fused into a single unitary structure.

United States Patent 1 Patel 11] 3,708,864 1 Jan. 9, 1973 [54] METHOD OFFORMING A WELD FITTING [75] Inventor: Hiralal V. Patel, Cleveland, Ohio[73] Assignee: The Weatherhead Company, Cleveland, Ohio [22] Filed: June22, 1971 [21] Appl. No.: 155,585

Related U.S. Application Data [62] Division of Ser. No. 885,018, Dec.15, 1969, Pat. No,

[52] U.S. Cl. ..29/479, 29/475, 29/478 [51] Int. Cl. ..B23k 31/02 [58]Field of Search....29/471.1, 474.3, 472.1, 473.3, 29/475, 478, 479

Primary ExaminerRobert D. Baldwin Assistant Examiner-Richard BernardLazarus Atiorney-McNenny, Farrington, Pearne and Gordon [57] ABSTRACT Acoupling for use in forminga welded tube joint is disclosed along with amethod for forming such joint. A thin coupling sleeve is tightlyswage-fitted onto the end of a tube to form a male or female tube endassembly suitable for engagement with a tubular mating part assemblywhich may be a fitting or another coupling sleeve and tube assembly. Themale-female interlocking arrangement provides radial and axial alignmentof the joined assemblies. The structure is arranged to provide a spacebetween the tube end face and the interior end face of the tubularmating part assembly. During the welding operation, external fusion heatis applied to form a single weld bead extending from the interior of thetube to the exterior surfaces of the assemblies. The width of the weldat its inner radial extremities is longer than the axial width of thespace between the interior end faces and its width at its outer radialextremities is at least equal to twice the axial length of themale-female telescoped portion so that all the members are fused into asingle unitary structure.

7 Claims, 4 Drawing Figures PATENTEDJAN 9 I975 3.708.864

1N VENTOR.

hop/21 44 l/ pnrez BACKGROUND OF THE INVENTION This invention relatesgenerally to tube couplings and more particularly to a novel andimproved welded tube coupling and a method for making such a coupling.

PRIOR ART Various types of welded tube couplings are known. For example,the U.S. Pat. Nos. 3,194,936; 3,248,l34; and 3,439,941 all relate tosuch couplings. The Nicol U.S. Pat. No. 3,439,941, assigned to theassignee of the present invention, illustrates a coupling arrangementwhich is particularly useful for use with high strength tubing such asprecipitation hardened stainless steel and the like. In the Nicolstructure, sleeves are positioned on the ends of tubes and the sleevesare provided with interfittihg mating end surfaces arranged to insureradial and axial alignment of the coupling halves prior to welding. Thesleeves cooperate to support the tube ends in the area of the connectingwelds so that the welded coupling provides a joint which is at leastsubstantially as strong as the tubing itself and is capable of reliablyabsorbing the loads applied to the tubing system.

Although couplings as disclosed by Nicol are very satisfactory for usewith tubing formed of many types of materials, difficulties aresometimes encountered when such a coupling arrangement is utilized inconjunction with tubing formed of materials having certain physicalproperties such as high notch sensitivity, relatively low rates of heatconductivity, and relatively high sensitivity to contaminationdifficulties. When, for example, the structure as disclosed in Nicol isutilized to join tubing formed of titanium or titanium alloys,difficulty can be encountered because such tubing is extremely notchsensitive and is susceptible to damage in the areas of any stressconcentrations. Similarly, the relatively thick wall thickness required,from a practical standpoint, in the sleeves of the Nicol device in orderto provide the male-female relationship illustrated therein, tends toresult in weld puddle control problems because of the high energy inputrequired for penetration of the thick section.

SUMMARY OF THE INVENTION A welded tube coupling in accordance with thepresent invention is particularly suitable for use with tubing formed ofmaterials which tend to have relatively high notchsensitivity, tend tohave a relatively low heat conductivity, and tend to be relativelysensitive to contamination problems.

In accordance with one embodiment of this invention, a coupling includestwo coupling halves each provided with a sleeve positioned around thetube end and axially located with respect thereto so that one sleeveprojects beyond the associated tube end and the other sleeve is spacedback from its associated tube end. This structure is arranged so that amale-female arrangement is provided in which the exterior of the surfaceof the tube of the male coupling is proportioned to telescope into thesleeve of the female coupling half to provide radial alignment betweenthe two coupling halves prior to welding. The ends of the sleeves abutto provide axial location between the two coupling halves.

In such embodiment, the structure is arranged so that the two tube endsare spaced a predetermined distance apart when the sleeve ends abut tofacilitate purging of the coupling to eliminate contamination problemsin the weld.

With this structure wherein the tube coacts with its associated sleeveto provide the only interfitting surfaces, the sleeve can be formed withsubstantially any desired thickness and can, if desired, be formed witha very thin wall section. Preferably, the relationship between the wallthickness of the sleeve and the wall thickness of the tube is selectedso that the sleeves provide sufficient support for the tube ends tocompensate for the weakening of the tube endmaterial caused by the heatof welding without providing excessive rigidity which would produceundesirable notch sensitivity problems. Further, such relationship canbe selected so that the amount of heat required to fuse the twocouplings together is not sufficiently high to cause puddle controlproblems. When the coupling in accordance with this invention is usedwith titanium or titanium alloy tubing, good results are obtained withthe wall thickness of the tubes is about three times the wall thicknessof the sleeve.

In accordance with the preferred method of assembling the sleeves on thetubes the sleeves are initially formed with sufficient clearance so thatthey can be easily slipped over the ends of the tube and the tube isthen radially expanded into tight engagement with the sleeve tofrictionally lock the sleeve with respect to the associated tube. Suchinternal swaging is particularly desirable when the sleeve has a wallthickness less than the wall thickness of the tube and results in anassembly wherein the tube is subjected to compressive stress while thesleeve is subjected to tensile stress to insure tight engagement alongtheir interface.

In accordance with another aspect of this invention at least the portionof the sleeves spaced from the weld are provided with a lubricant filmso that radial support can be provided for the tube without producingstress concentrations or wear even when the loading applied to thetubing system tends to produce relative movement between the sleeve andtube. Such a lubricating film is particularly desirable when thematerials forming the coupling have a tendency to gall and fret whenrelative sliding movement between surfaces occur. For example, titaniumtends to present this problem and the lubricating film virtuallyeliminates such problem.

BRIEF DESCRIPTION-OF THE DRAWINGS FIG. 1 is a longitudinal section oftwo pieces of tubing fitted with the female and male coupling sleeves ofthis invention prior to roll swaging with one tube broken away toillustrate the lubricating coating;

FIG. 2 is a longitudinal section similar to FIG. 1 after the rollswaging process has been performed to lock the sleeves on theirassociated tubes;

FIG. 3 is a longitudinal composite section illustrating in its upperportion the coupling halves positioned for welding and in its lowerportion the completed welded connection; and

FIG. 4 is a composite view, partially in longitudinal DETAILEDDESCRIPTION OF THE DRAWINGS Referring to FIGS. 1 through 3 of thedrawings in greater detail, two similar pieces of tubing 10 and 12fitted with coupling sleeves 14 and 16 so as to form a female couplinghalf assembly 13 and a male coupling half assembly 15. The couplingsleeve 14 is initially formed with central bore 18 having a suitablediameter so as to slip over the tube 10 with a relatively close fit. Asillustrated in FIG. 1 the axially extending portion 20 of the sleeve 14is outwardly flared to an appropriate degree so that when the tube 10 isexpanded by roll swaging to the assembled condition illustrated in FIG.2, the axially extending'portion 20 and the remaining portion of thesleeve 14 have a substantially cylindrical configuration. As shown inFIG. 2, the sleeve 14 has an expanded inside diameter substantiallyequal to the outside diameter 24 of the expanded adjacent tube 10 alongthe entire sleeve length. The drawings exaggerate the degree ofexpansion for illustration purposes and it should be noted that the tubemember is preferably expanded so as to obtain about 3 to percentreduction in wall thickness when the tubing is formed of titanium or thelike.

The male assembly or coupling half 15 is formed by the tube l2'and thesleeve 16. The sleeve 16 is also initially formed with a central bore 26proportioned to slip over the tube 12 with a relatively close fit. Thesleeve 16 is properly positioned around the tube 12 so as to provide acircumferential exterior recess, generally indicated at 28. The tube 12is similarly expanded by roll swaging into the sleeve 16 so as toprovide an expanded outside tube diameter 30 substantially equal to theoutside tube diameter 24 of the expanded female assembly 13 as shown inFIG. 2.

The axially extending portion 20 of the sleeve 14 has a greater axiallength as measured from the end face 32 of the adjacent tube to the endsurface 34 of the extending portion than the corresponding axial depthof the circumferential exterior recess 28 as measured from the end face36 of the tube 12 to the end surface 38 of the adjacent sleeve 16. Thetelescoped portion of the mating assemblies has an axial length of fromabout 0.030 to about 0.040. However, the drawings exaggerate thedimensions for purposes of clarity. When the mating assemblies areplaced in abutting engagement, the interior tub end faces 32 and 36 areseparated by a space 40, defined by the end faces 32 and 36, and theinterior surface of the sleeve 14, as best shown in the upper portion ofFIG. 3. The space 40 has an axial length of about 0.002 to 0.006 inchesand this dimension has again been exaggerated in the drawing forpurposes of clarity. This space is provided to facilitate an inert gaspurge prior to the welding operation so as to prevent contamination ofthe weld.

When the interfitting mating surfaces of the assemblies are engaged,axial and radial alignment is assured. Radial alignment is necessarybefore the end of the tube 12 can move into the sleeve 14. Similarly,the tubes must be axially aligned if the two sleeve end faces 34 and 38engage around the entire periphery. Therefore, a visual inspection canbe used to determine if the two halves are properly positioned.

When the mating assemblies are properly engaged,

as determined by visual or manual inspection, the joint formed by theabutting end surfaces 34 and 38 of 'the coupling sleeves 14 and 16 willlie in a predetermined spaced relationship with respect to the space 40-between the end faces 32 and 36 of the tube members 10 and 12 Thus, thejoint also serves as a visual means to accurately locate the electrodeduring a fusion welding process Accordingly, the mating assembly membersmay be joined by a single weld bead 42 produced by externally applyingfusion heat substantially along the joint, as shown in the lower portionof FIG. 3. The weld bead extends from the inner surface of the tubemembers to the exterior surfaces of the assemblies. The width of theweld bead at its inner radial extremity is larger than the width of thespace 40 previously separating the tube end faces and the tube membersare also fused by the single weld. At the exterior surfaces of theassembly, the width of the weld bead 42 is at least equal to about twicethe axial spacing between the space 40 and the sleeve end surfaceso-that a single unitary structure results.

The following are examples of specific dimensions which have been usedfor the manufacture of a welded tube coupling for titanium tubing. Thesleeves in each case were formed of the same material as the tube. For a3/16 inch tubing having a wallthickness of 0.0l6 inches, the sleeveswere provided initially having an inside diameter of about 0.193 inchesand a wall thickness of about 0.07 inches. The male sleeve length wasabout 0.25 inches and the female sleeve length was about 0.31 inches. Inanother weld coupling for /8 inch titanium tubing having a wallthickness of 0.036 inches, the sleeves were provided with an insidediameter of about 0.632 inches and a wall thickness of about 0.014inches. In this instance, the male sleeve had a length of about 0.657inches and the female sleeve had a length of about 0.7 l 7 inches.

In each of the above examples the sleeves were p ositioned over the endsof the associated tubes andthe tubes were internally swaged toincreasetheir diameter until the thickness of the tube wall was reduced about 4percent.

As illustrated in the above embodiment of this invention, themale-female interlocking arrangement characterized by single lip matingpermitted the use of a coupling sleeve having a wall thicknesssubstantially less than that of the adjacent tube and approaching.

about one-third the thickness thereof. Consequently, the total wallthickness was not greatly increased and stress concentration problemswere not particularly significant. A coupling in accordance with thisinvention provides support in the heat weakened weld zone with a minimumincrease in the stress concentration problems. In addition, thereduction in total wall thickness at the weld location, as compared tocoupling arrangements formerly known in the art, alleviates the weldpuddle problem since less heat is, required to penetrate the total wall.

Another embodiment of this invention is illustrated in FIG. 4, whichshows an expanded tube identical in structure to the tube 12 and asleeve identical to the sleeve 16, as shown in FIGS. 2 and 3. However,in this embodiment, the coupling connects the tube to an elbow fitting44. Of course, other types of fittings can be provided and the elbow 44is illustrated only by way of example. The elbow 44 has a central bore46 having a diameter equal to the inner diameter of the tube 12. Asshown in FIG. 4, the elbow provides a female mating assembly in thisembodiment and includes an axially extending portion a having an endsurface 34a abutting the end surface 38 of the sleeve 16 in a fashionidentical to that of the above embodiment. The axially extending portion20a and the circumferential exterior recess are similarly proportionedso that a space 40a exists between the end face 36 of the tube 12 andthe end face 32a which corresponds to the end face of the tube 10 in theabove embodiment.

The mating assemblies again provide for precise axial and radialalignment which may be visually inspected by the joint formed by theabutting end surfaces 34a and 38 on the outer periphery of the assembly.The space 40a is similarly provided to facilitate purging the weld areawith a suitable gas. THe mating assembles, specifically the elbow 44,the tube 12, and the sleeve 16 are joined by a single fusion weld bead42a illustrated in the lower portion of FIG. 4. The weld bead 42a has alarger axial width at its inner extremities than the space 40a and awidth at the outer surface of the mating assemblies at least equal toabout twice the axial spacing between the space 40a and the abutting endsurfaces 340 and 38, so that the mating assemblies are joined in amanner identical to that in the above embodiment. Although theembodiment illustrated in FIG. 4 provided the female assembly, it mayhave similarly provided the male assembly.

In many systems the tubing is subjected to vibration and/or torsionalloads which tend to produce twisting and bending of the tube. Since thesleeves are anchored only at the weld interface such loading is notdirectly applied along the length of each of the sleeves and relativemovement tends to occur between the sleeves and the adjacent tubesurfaces with the amount of movement increasing with increased spacingform the weld. In many such instances, it is very desirable to provide alubricating coating 49 (illustrated in FIG. 1) along the interengagingsurfaces between each sleeve and the associated tube, at least along theinterface at locations spaced from the weld. This is particularlydesirable when the coupling is used to join materials such as titaniumwhich tend to gall or fret under working conditions. Preferably, theinterior portion of each sleeve. extending axially from the end surfaceremote from the tube end for a distance equal to about one-fourth toone-half of the total sleeve length is provided with a dry lubricantcoating 49. I

Because the sleeve is subjected to relatively high temperatures duringwelding normal liquid film lubricants are not generally satisfactory.For this reason, it is preferable to use a dry lubricant film in whichfinely divided solid lubricant materials are dispersed in a bondingvehicle. Such vehicle is usually organic and serves to hold thelubricant material in place at least until the welding is completed. Thebinder by be of the type that drys such as by solvent evaporation, withor without the application of heat, or may be of a type which is curedby a chemical reaction.

Under the thermal conditions occurring during welding, the binder maypartially or completely decompose. However, since a tightinterengagement is provided along the interface in which the lubricantis located, it is not necessary in all instances for the binder tomaintain its binding function since such interengagement will retain thelubricant in place.

The solid lubricants may be of any known type such as M05 Sb O orgraphite or mixtures thereof. The resin binder may be any film formingmaterial of a type known to those in the art. A satisfactory lubricatingfilm has been obtained by surface treatment of the sleeve which employeda vapor blast with 220 grid aluminum oxide before applying the drylubricant coating. A coating consisting of an epoxy bonded dry filmlubricant containing MoS and Sb O was then applied according to theprocess identified as Dow-Corning Process No. 1-3930. It was found thattitanium couplings provided with such coating, when compared to similarcouplings without the coating, were capable of absorbing far greaternumbers of cycles of vibration and loading without failure.

Preferably, the coating is applied along both the inner and outersurfaces of each sleeve. When this is done the coating along theexterior surface provides a visual indication which may be used toproperly orient the sleeve with respect to the tube during assembly. Thecoating may be applied to the tube end underlying the sleeve. However,in most cases such coating on the tube should terminate at a locationspaced from the end of the tube so that the coating does not contaminatethe weld.

In order to minimize the presence of stress concentration, it is alsopreferable to provide a generous radius 54 along the inner surface ofeach of the sleeves adjacent to their ends remote from the weld. THisradius eliminates the sharply defined boundary line between the sleevesand the adjacent tube and thereby minimizes the presence of stressconcentrations.

Although preferred embodiments of this invention are disclosed, it is tobe understood that various modifications and rearrangements of parts maybe resorted to without departing from the scope of the inventiondisclosed.

What is claimed is:

l. A method of forming a welded joint between a tube and a tubularmating part assembly, comprising forming a tube end assembly includinga'tube extending to an end face, positioning a sleeve having an endsurface around said tube tightly engaging the outer surface thereofalong an interface therebetween and adjacent to one-end of said tube sothat said tube end assembly includes said end face extending radiallyoutward from the inner surface of the tube and an end surface extendingradially inward from the outermost surface of said tube end assembly ata location axially spaced from said end face and a cylindrical surfaceextending between the associated end face and end surface, placing saidtube end assembly in abutting engagement with said tubular mating partassembly also having an interfitting similar end face, end surface andcylindrical surface proportioned to telescope with said cylindricalsurface of said tube end assembly so as to axially and radially alignsaid assemblies, providing a greater axial spacing between said end faceand end surface of one of said assemblies than that of the otherassembly so that said end faces are spaced when said end surfaces are inabutting engagement, and applying fusion heat along the joint betweensaid abutting end surfaces to form a single weld bead extending theentire radial distance from the inner surface of said tube to the outersurface of said assemblies and having a width at said inner surface atleast equal to the spacing between said end faces and a width at theouter surface at least equal to twice said axial spacing between saidend face and end surface so that the weld encompasses both the end facesand the end surfaces.

2. A method of forming a welded joint as set forth in claim 1 whereinsaid mating part assembly is formed by a second tube and a second sleevepositioned around said tube in tight engagement therewith.

3. A method of forming a welded joint as set forth in claim 1 whereinsaid sleeve is initially formed to freely fit over said tube and issecured to said tube by swaging said tube from its inside to increasethe diameter of said tube and cause tight engagement between said sleeveand tube.

4. A method of forming awelded joint as set forth in claim 3 whereinsaid sleeve projects beyond said end face to provide a projectingportion, said projecting.

portion before swaging is flared outward and said swaging increases thediameter of said sleeve until said projecting portion is cylindrical.

5. A method of forming a welded joint as set forth in claim 1 wherein alubricating film is applied along a substantial axial portion of saidinterface, said lubricat-

1. A method of forming a welded joint between a tube and a tubularmating part assembly, comprising forming a tube end assembly including atube extending to an end face, positioning a sleeve having an endsurface around said tube tightly engaging the outer surface thereofalong an interface therebetween and adjacent to one end of said tube sothat said tube end assembly includes said end face extending radiallyoutward from the inner surface of the tube and an end surface extendingradially inward from the outermost surface of said tube end assembly ata location axially spaced from said end face and a cylindrical surfaceextending between the associated end face and end surface, placing saidtube end assembly in abutting engagement with said tubular mating partassembly also having an interfitting similar end face, end surface andcylindrical surface proportioned to telescope with said cylindricalsurface of said tube end assembly so as to axially and radially alignsaid assemblies, providing a greater axial spacing between said end faceand end surface of one of said assemblies than that of the otherassembly so that said end faces are spaced when said end surfaces are inabutting engagement, and applying fusion heat along the joint betweensaid abutting end surfaces to form a single weld bead extending theentire radial distance from the inner surface of said tube to the outersurface of said assemblies and having a width at said inner surface atleast equal to the spacing between said end faces and a width at theouter surface at least equal to twice said axial spacing between saidend face and end surface so that the weld encompasses both the end facesand the end surfaces.
 2. A method of forming a welded joint as set forthin claim 1 wherein said mating part assembly is formed by a second tubeand a second sleeve positioned around said tube in tight engagementtherewith.
 3. A method of forming a welded joint as set forth in claim 1wherein said sleeve is initially formed to freely fit over said tube andis secured to said tube by swaging said tube from its inside to increasethe diameter of said tube and cause tight engagement between said sleeveand tube.
 4. A method of forming a welded joint as set forth in claim 3wherein said sleeve projects beyond said end face to provide aprojecting portion, said projecting portion before swaging is flaredoutward and said swaging increases the diameter of said sleeve untilsaid projecting portion is cylindrical.
 5. A method of forming a weldedjoint as set forth in claim 1 wherein a lubricating film is appliedalong a substantial axial portion of said interface, said lubricatingfilm extending from the end of said sleeve remote from said end surfacealong such interface toward said end surface and terminating at alocation spaced from said end surface.
 6. A method of forming a weldedjoint as set forth in claim 5 wherein said lubricating film is a dryfilm coating applied to said sleeve.
 7. A method of forming a weldedjoint as set forth in claim 5 wherein said lubricating film is a dryfilm coating applied to said tube.